diff --git a/pkg/camerrors/errors.go b/pkg/camerrors/errors.go
index 1ff9b8cbc..4934d974d 100644
--- a/pkg/camerrors/errors.go
+++ b/pkg/camerrors/errors.go
@@ -22,4 +22,7 @@ import (
 	"errors"
 )
 
-var MissingKeyBlob = errors.New("key blob not found")
+// ErrMissingKeyBlob is returned by the jsonsign handler when a
+// verification fails because the public key for a signed blob is
+// missing.
+var ErrMissingKeyBlob = errors.New("key blob not found")
diff --git a/pkg/jsonsign/verify.go b/pkg/jsonsign/verify.go
index 651b9df5f..d8513c7d1 100644
--- a/pkg/jsonsign/verify.go
+++ b/pkg/jsonsign/verify.go
@@ -138,11 +138,11 @@ func (vr *VerifyRequest) ParsePayloadMap() bool {
 func (vr *VerifyRequest) FindAndParsePublicKeyBlob() bool {
 	reader, _, err := vr.fetcher.FetchStreaming(vr.CamliSigner)
 	if err != nil {
-		log.Printf("error fetching public key blob: %v", err)
+		log.Printf("error fetching public key blob %v: %v", vr.CamliSigner, err)
 		// TODO(mpl): we're losing some info here, so maybe
 		// create an error type that contains the reason,
 		// instead of logging the reason.
-		vr.Err = camerrors.MissingKeyBlob
+		vr.Err = camerrors.ErrMissingKeyBlob
 		return false
 	}
 	defer reader.Close()